In recent years, in the fields of semiconductor, optical/magnetic recording, etc., as demands for higher density, higher integration and others have increased, techniques have become essential for fine pattern processing of about several hundreds to tens of nanometers or less. Therefore, to achieve the fine pattern processing, elemental techniques of each process have been studied actively such as a mask, stepper, exposure and resist material.
For example, in the process of masking and stepper, studied are the technique of using a specific mask called the phase shift mask to provide the light with a phase difference, and increasing fine pattern processing precision by the effect of interference, the liquid immersing technique of filling a liquid into between the stepper lens and wafer, largely refracting the light passed through the lens, and thereby enabling the fine pattern processing, and the like. However, the former technique requires enormous cost to develop the mask, the latter technique requires expensive equipment, and thus, it is significantly difficult to reduce the manufacturing cost.
Meanwhile, many studies have proceeded also on the resist material. Currently, the most common resist material is the photoreactive organic resist (hereinafter, also referred to as a photoresist) that reacts by an exposure light source such as ultraviolet light, electron beam and X-rays (hereinafter, see Patent Document 1 and Non-patent Document 1).
In the laser light used in exposure, the intensity of the laser light focused by the lens generally shows the Gaussian distribution form as shown in FIG. 8. At this point, the spot diameter is defined by 1/e2. In general, the reaction of photoresist starts by absorbing energy represented by E=hν (E: energy, h: Planck constant, ν: wavelength). Accordingly, the reaction is not dependent on the intensity of the light significantly, and rather dependent on the wavelength of the light, and thus, the reaction occurs in the entire portion (exposed portion) irradiated with the light. Therefore, when the photoresist is used, the photoresist is faithfully exposed with respect to the spot diameter.
The method of using a photoreactive organic resist is an extremely useful method in forming fine patterns of about hundreds of nanometers, and since the photoresist using photoreaction is used, to form finer patterns, it is necessary to expose with a smaller spot than a pattern required in principle. Accordingly, it is indispensable to use a KrF laser, ArF laser or the like with short wavelengths as an exposure light source. However, these light source apparatuses are large-size and expensive, and are unsuitable from the viewpoint of reducing the manufacturing cost. Further, in the case of using the exposure light source of electron beam, X-rays or the like, since it is necessary to evacuate the exposure atmosphere to a vacuum state, using a vacuum chamber is required, and there are significant limitations from the viewpoint of the cost and increases in the size.
Meanwhile, when a substance is irradiated with the laser light having the distribution as shown in FIG. 8, the temperature of the substance also shows the same Gaussian distribution as the intensity distribution of the laser light (see FIG. 9). At this point, when a heat-reactive resist is used that is a resist reacting at some temperature or more, as shown in FIG. 9, since the reaction proceeds only in the portion becoming a predetermined temperature or more, it is made possible to expose the range smaller than the spot diameter. In other words, without shortening the wavelength of the exposure light source, it is possible to form the pattern finer than the spot diameter, and by using the heat-reactive resist, it is possible to reduce the effect of the wavelength of the exposure light source.
In the field of optical recording, the technique is reported that WOx, MoOx, other chalcogenide glass (Ag—As—S series) or the like is used as a heat-reactive resist, and exposed with a semiconductor laser or 476-nm laser to form the fine pattern (hereinafter, see Patent Document 2 and Non-patent Document 2). These optical disks used in the optical recording field are a generic name for media for applying laser light to the disk coated with the resist material and reading the information recorded in fine asperities provided on the disk surface, and as decreases the pitch between recoding units called the track pitch, the recording density increases, and the data capacity recordable per area increases. Therefore, to improve the recording density, studies are made on techniques for fine concavo-convex pattern processing using the resist material. However, the studies using the heat-reactive resist cope with the demand for narrowing the pitch of the pattern in the film surface direction (for improving the recording density of information), and there has been no demand for forming deep grooves in the film thickness direction. Meanwhile, in recent years, the demand for application using a pattern shape with a deep groove depth has increased in other fields. As the depth of the groove in the film thickness direction, the thickness of the film of the heat-reactive resist itself is the depth of the groove in the depth direction, and therefore, to form deep grooves, it is necessary to thicken the heat-reactive resist. However, by the film thickness increasing, uniformity in the film thickness direction by exposure loses, and as a result, there is the problem that the processing precision of the fine pattern degrades not only in the depth direction but also in the film surface direction.
Then, a technique of beforehand forming a film (hereinafter, also referred to as an etching layer) with a thickness corresponding to the groove depth desired to form under the heat-reactive resist film, and forming deep grooves in the film under the resist using the heat-reactive resist provided with a pattern shape by being exposed and developed as a mask is considered. Generally, to etch uniformly in the depth direction, processing by dry etching is used. For example, when SiO2 is used for the etching layer, it is possible to perform dry etching using fluorocarbons. In the case of processing by dry etching, the resist material used as a mask is required to have resistance to dry etching of fluorocarbons as well as permitting the fine pattern processing. As described above, as an example of substituting the heat-reactive resist material researched in the field of optical recording, WOx and MoOx are reported previously. In these heat-reactive resists, when dry etching is performed using fluorocarbons, WOx that is disclosed has etching resistance only less than three times (a value obtained by dividing the etching rate of SiO2 by the etching rate of WOx) that of SiO2, and is insufficient as a mask material to form deep grooves (hereinafter, see Non-patent Document 3).
Meanwhile, layered product materials in which Ag, Cu and their compounds having relatively high dry etching resistance, and oxides (limited to part of materials among published materials) having dry etching resistance are used as heat-reactive resists are disclosed, and an etching layer is layered under the resist (hereinafter, see Patent Documents 3 and 4). In the former compounds, the resist material is sublimated using ultraviolet rays to form the pattern, and then, by performing dry etching, deep grooves are formed. However, in the layered product Ag (resist layer)/As3S2 (etching layer) disclosed in the Example, As3S2 is sublimated first by heating, and reaching the intended process is not achieved. Meanwhile, in the latter compounds, coagulation, core formation and decomposition actions are induced to the oxide material by heat, light or gas reaction and so on a sea-island pattern is formed, and then, by performing dry etching, deep grooves are formed. However, only a random sea-island structure can be formed, and it is difficult to control the pattern size of a fine pattern with uniform concavo-convex structure, line shapes and the like.